I am sending out transactional emails in my app and was reading up on best practices (for spam reasons obviously) and the following strikes me as odd.
I was expecting notification emails from Google, Facebook etc to have simple sender addresses like [email protected]/[email protected] etc.
But the actual addresses seem to be [email protected], [email protected] etc
Is there any reason, technical or otherwise, for not having a single/simple sender address when sending out transactional emails to all users?
While I can't speak to Facebook and Google specifically, the main reason for this is tracking and parsing of bounce notifications.
If you look at the headers you will see the 'Return-Path' is the same - [email protected] - this address is where mail servers should send automated bounces for NDR (non-delivery), such as 'inbox full' or 'nonexistent address', although some systems will use the 'From' as well, hence what you see.
The 'hash' part is often a structured piece of data that may help guide to particular clusters, determine the type of email, or identify recipients. You will often find ticketing systems use the same method to ensure your messages are directed to the same support agent if you reply.
While you could technically use the Message-ID header for this, that header tends to be a non-colliding 'random' hash rather than specifically structured data to assist routing without relying purely on lookup tables.